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With the SPDR S&P Biotech Index up 25% over the trailing-12-month period, it's evident that investment dollars are willingly flowing into the biotech sector. Keeping that in mind, let's have a look at some of the rulings, studies, and companies that made waves in the sector last week.

It was a generally positive week within the biotech sector, with four of the five most notable stories sending these stocks higher. Therefore, if you need a pick-me-up on this, the first down week of the year for the market indexes, you've come to the right place.

The big news of the week came just yesterday with the FDA approval of Kadcyla, previously known as T-DM1 and developed by Roche and ImmunoGen . Kadcyla was approved as a treatment for HER2-positive breast cancer and is unique in that it includes ImmunoGen's targeted antibody payload technology which helps deliver more potent doses of a chemotherapy toxin specifically to tumor cells while minimizing healthy cell damage. Investors have been generally unhappy with the nominal royalties ImmunoGen is set to receive from the sale of the drug, but I consider it just the tip of the iceberg for this rapidly growing biotech company.

Repros Therapeutics , on Thursday, came out with positive news that the FDA has given the company the go-ahead to complete its ongoing study of Androxal as a secondary treatment for hypogonadism as originally planned. If you recall, Repros disclosed just weeks ago that one of its testing groups exhibited anomalous results which necessitated its top-line data be pushed back one quarter. This week's news gives Repros the clearance by the FDA to assess the data both with, and without, this group of patients. In a few more months, we'll find out if investors are rewarded or run over the coals for their patience.

Similarly, Chelsea Therapeuticsshot out of a cannon mid-week following word that the FDA would allow it to resubmit hypotension drug Northera using data from its earlier clinical studies. Originally, Chelsea was told in March 2012 that it would need to conduct further studies of Northera, but an appeal made to the director of the Office of New Drugs of the FDA proved successful. With Chelsea successfully redefining the end goal of its study, it was able to demonstrate a short-term clinical benefit to the drug of about one week. Beyond that, the data was less defined. This news saves Chelsea big time in their pocket book and the company plans to resubmit its NDA in the second quarter.

Gilead Sciences produced a fourth positive late-stage study of all-oral hepatitis-C drug Sofosbuvir on Tuesday, and, not surprisingly, the drug excelled again. This time Gilead tested Sofosbuvir on the less common genotypes 2 and 3 and produced cure rates of 50% after 12 weeks and 76% after 16 weeks -- far and away better than the current standard treatment. With all four late-stage trials showing significant clinical benefits with an equal or better safety profile, an approval looks all but in the bag.

The one "Debbie downer" of the sector this week was anti-obesity drug maker VIVUS , which received word from the European Medicines Agency's Committee for Medicinal Products for Human Use on Thursday that it had, again, decided to uphold its rejection of Qsvia (the European marketing name for Qsymia) for the treatment of chronic weight management and rejected VIVUS' appeal. The EMA's panel suggested that it would like to see how Qsvia affects the cardiovascular system in trials before recommending the drug. While not a real shock, it nonetheless reinforces what a tough road it'll be for weight-loss management drugs to crack the European market.

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